[RTTY] K3 reduced-bandwidth RTTY analysis

[Joe Subich, W4TV]

On 3/22/2013 1:07 PM, Jay WS7I wrote:
> Guess you missed the point. Andy's work was with the K3 which he no
> doubt owns and likes.

I'm afraid you missed *my* point.

Andy's work with the K3 provides a false picture of the benefits of
"shaped" AFSK because most of the rigs being used for AFSK do not
have the same 400 Hz "AFSK" filter as the K3 to clean up distortion
introduced by overdriving the mic preamp/modulator or hum/RFI that
might contaminate the audio.

Elecraft deserve high marks for their effort to make sure transmitted
RTTY is as clean as it can be - whether the user chooses FSK or AFSK.
However, I don't see any other manufacturer making the same commitment
to creating clean signals.

Unfortunately, I don't see anyone raising the issue of transmit purity
with Ikensu transceivers in general.  Andy's work was done with the K3
and essentially gave the other manufacturers a pass on AFSK by not
showing what happens in *analog* transceiver that do not have a narrow
post-modulator filter to clean up AFSK the way the K3 does.

Similarly, even ARRL (most specifically W3IZ's review in the current
issue of QST) do not make the slightest mention of signal purity issues
like the absolutely horrible transmit phase noise spectrum of the new
FT-3000.  Such problems render *any* wave shaping or even careful audio
management moot - whether AFSK, FSK or even phone/CW.

> The RTTY community should appreciate those folks who are testing and
> enhancing our mode of operation. Folks like Andy, Chen, David have
> done more in the last couple of years for RTTY than a lot that went
> on before.

I don't think there is anyone who understands the issues that doesn't
appreciate the work of folks like Chen, Andy, David and many others
who have worked to enhance RTTY.  The  only thing I'm saying is that
some of the work gives a false impression that the only thing necessary
to turn a dirty Ikensu into an on-air "good neighbor" is to switch to
AFSK with cocoamodem, 2tone or the proper TXBPF in MMTTY.  That's far
from the case with so many AFSK users running sound cards into the mic
jack and turning "all knobs right" as recommended in the "manuals" of
many interfaces.

I've written many times about the need to use sound cards that are
clean, sound cards that are not used for operating system sounds
(just yesterday afternoon/evening, I heard someone streaming a radio
feed across 21.070 for several hours), use the rig's high level input
and disconnect the microphone, etc.  There is no "magic bullet" for
a cleaner RTTY signal but most users can avoid the mistakes if they
motivated are shown how - rather than assuming that the newest software
will automatically fix everything.

73,

    ... Joe, W4TV


On 3/22/2013 1:07 PM, Jay WS7I wrote:
> Guess you missed the point.  Andy's work was with the K3 which he no
> doubt owns and likes.  FLdigi no doubt has facilities to do testing for
> their software and I have major doubts that their are thousands of folks
> running AFSK RTTY on anything in any case.
>
> The major thing is that the K3 Folks like FlDigi and others are willing
> to make changes.  Doubt that Icom, Yaesu, Kenwood are listening much in
> the RTTY reflector.  A lot of folks choose the K3 just because they
> listen and are willing to make changes.
>
> The RTTY community should appreciate those folks who are testing and
> enhancing our mode of operation.  Folks like Andy, Chen, David have done
> more in the last couple of years for RTTY than a lot that went on
> before.  Us old pharts that are in love with narrow filters, FSK, are
> starting to learn that the soundcard has some major advantages heck I
> might even have to retire my Hal ST-8000 and my old trusty FT-1000D.  I
> can feel a K3 and a fancy soundcard in my future.  Maybe even a fancy
> interface tho I have to retire these opto's.
>
> On 3/22/2013 9:41 AM, Joe Subich, W4TV wrote:
>> The one fault I found with Andy's AFSK work is that he used the K3
>> with AFSK filter which means his results are not typical of those one
>> would find with fldigi or 2tone and the tens or thousands of IC706,
>> IC-746/756/7000/76000, FT-1000MP/2000/3000/5000, TS-2000/870/570, and
>> older rigs that represent the majority of transceivers in use today.
>
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